$2526\mathrm{.}26$ Civil engineering relies on foundational theories to address complex challenges in infrastructure and construction. Structural mechanics, material science, and fluid dynamics form the bedrock of this discipline, guiding the design and analysis of bridges, buildings, and transportation systems. Geotechnical principles underpin soil behavior and foundation design, while environmental theories inform sustainable development practices. With a solid theoretical base, civil engineers innovate solutions for urbanization, climate change resilience, and resource management. Understanding these theories is paramount for advancing the field and ensuring the safety and functionality of our built environment.